Tablets, capsules, caplets and many other types of devices have been used for dispensing a beneficial agent to a fluid environment of use. Easy manufacture of a device that provides for prolonged delivery of an active agent in a controlled and predictable manner continues to be a goal, especially in the area of drug delivery.
U.S. Pat. No. 4,290,426 to Luschen et al describes a cylindrical dispenser for releasing a beneficial agent into a fluid environment at a rate that is governed by the fluid induced relaxation of a polymeric agent contained within the dispenser. The cylindrical dispenser includes an impermeable container that has within it a reservoir and a passageway from the reservoir to the exterior of the container. The reservoir contains a polymer and a beneficial agent. The polymer imbibes fluid from the environment and thereby undergoes relaxation, releasing the beneficial agent from the device. The amount of agent released is dependent on the rate of relaxation of the polymer over time.
Coated dosage forms have also been suggested for delivery of a controlled amount of a beneficial agent over a prolonged period of time. U.S. Pat. No. 5,256,440 describes a process for producing a film coated dosage form. A continuous groove is inscribed in a dosage form core. A latex film is coated onto the core, the groove defining a fixed zone and a detachable zone for the film. The detachable portion of the latex film detaches when it is exposed to the environment of use, thereby exposing a discrete portion of the dosage form core surface. The remainder of the film remains attached to the dosage form core. The exposed portion of the dosage form surface erodes and releases active agent to the environment of use.
Coated tablets for constant and prolonged drug release are described by Conte et al in J. Controlled Release, Vol. 26, (1993) pages 39-47. These GEOMATRIX.TM. Systems are swellable matrices that are coated or tableted with polymeric barrier layers. Release performances of the systems are modulated as a result of the restriction of the releasing surface by the polymeric barrier layer coatings. As the extent of coating of the system's surface is increased, the release kinetics of the system shift toward constant release. These systems are further described in U.S. Pat. No. 4,839,177 to Colombo et al.
As can be observed in the above-referenced patents and publications, devices have been described that provide for prolonged delivery of an active agent. However, there remains a continuing need for improved systems for delivering an active agent in a reliable and reproducible manner that are easy and inexpensive to manufacture.